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Jerry Lile <br /> July 11, 2002 <br /> Page 3 <br /> CONCLUSIONS <br /> HERD evaluated the December May 9, 2002, "Response to Comments-January 2, 2002 Letter, <br /> Pombo Property, Tracy, California"prepared for Chevron by Geomatrix Consultants located in <br /> Oakland, CA. Limitations on the data discussed above create uncertainty in the estimated risks. <br /> Using the 95%UCL soil concentration and the maximum detected groundwater concentration, the <br /> total screening level risk to residential receptors is 2 x 10-6 with potential future groundwater <br /> exposure contributing a risk of 2 x 10-6 and potential soil exposure contributing a risk of 2 x 10-7. <br /> The total hazard index is less than 1. While the total risk is in excess of the benchmark target of 1 x <br /> 10-6, it falls within the range of 1 x 10-4 to 1 x 10-6 leaving the acceptability of the risk as a risk <br /> management decision. <br /> Please contact me at (916) 255-6633 if you have any questions. <br /> Reviewed by: David L. Berry, Ph.D. <br /> Senior Toxicologist <br /> Science,Pollution Prevention and Technology Program <br /> Human and Ecological Risk Division <br /> cc: Wendy L. Cohen <br /> Chief, Private Sites Cleanup Unit <br /> California Regional Water Quality Control Board <br /> Central Valley Region <br /> 3443 Routier Road, Suite A <br /> Sacramento, CA 95827-3098 <br /> tile:020605j l.doc.6hr <br /> i <br /> I <br />